1. Field of the Invention
The present invention generally relates to a reversible recording material and an electrochromic displaying element using the reversible recording material in which color is reversibly changed by a voltage being applied from an external device. In addition, the present invention can be applied to a reflection type display and electronic paper.
2. Description of the Related Art
Recently, as a recording medium to replace paper, electronic paper has been greatly developed. When the electronic paper is compared with existing displays such as a CRT (cathode ray tube) and an LCD (liquid crystal display), the electronic paper is a flexible reflection type displaying device. Further, the electronic paper has characteristics such as high white reflectance, a high contrast ratio, high definition image displaying ability, power saving by a memory effect, thin and light-weight, and low cost.
In order to realize the electronic paper, many methods can be used, for example, an electrophoresis method or a liquid crystal using method. Of the methods, when a method is used which utilizes a chromic material, the electronic paper has high white reflectance, a high contrast ratio, and visibility near to paper. Therefore, the chromatic material utilizing method has high potential for realizing the electronic paper. The chromic materials are classified into many types depending on image forming methods. As representatives, there are an electrochromic material and an acid-based chromic material using, for example, a leuko dye. Especially, an electrochromic displaying element, which utilizes color development and color reduction of an electrochromic compound, is a reflection type displaying element, has a memory effect for power saving, and can be driven by a low voltage. Therefore, the electrochromic displaying element has been researched and developed in a range from material development to device designing, as a candidate for the electronic paper.
From a viewpoint of materials, of compounds which have a chromic phenomenon, a styryl-based pigment (compound) has high color development characteristics, and can develop various colors depending on the material structure. Therefore, the styryl-based pigment has been expected to realize a multiple color displaying element. The styryl-based compound shows characteristics such as color development and reduction by acid base, by light, and by electric oxidation reduction, and has been researched as an electrochromic material which is used for an electrochromic displaying element. However, the durability of the styryl-based compound is not sufficient and the electrochromic displaying element using a styryl-based compound has not been put into practical use (refer to Patent Document 1).
In addition, as an electronic device including electronic paper, an electrochromic device has been greatly researched in which an electrochromic material is formed on semiconductor particles. For example, in Patent Document 2, an electrochromic compound is adhered onto a nano-crystalline layer disposed on an electrode. Conventionally, similar to Patent Document 2, in many cases, an acid group tail of, for example, carboxylic acid and salicylic acid of an organic functionality material is adhered onto a hydroxyl group of inorganic fine particles. When the acid group tail is used, an organic compound can be adhered onto the hydroxyl group of the inorganic fine particles. However, since the bonding force between them is not sufficient, while the device is being manufactured, after the formed device is repeatedly used, or under alkaline conditions, the bonding between the organic compound and the inorganic fine particles is easily broken.
[Patent Document 1] Japanese Patent No. 60-024829
[Patent Document 2] Japanese Translations of PCT International Publication No. 2000-506629